Numerous mechanisms have been used in automatic warehouses for transferring pans or articles between a selected storage compartment in a storage unit containing a number of such racks and compartments and an elevator mechanism or shuttle which carries the pan or article to a predetermined location. These retrieval or extractor devices use various mechanisms for engaging the pan and for moving the pan between the storage compartment and elevator. For example, certain retrievers use an electromagnet which clamps onto a metal pan or plate attached to the pan whereas other retrievers use a pneumatic or suction cup device for grasping the pan. Still other devices use a mechanical arm or latch which mechanically engages a bracket or flange mounted on the front wall of the pan. Certain other types of pan transfer devices use pins mounted on chains or rams which engage the pan for transferring the same between the elevator and storage compartment.
Although many of these prior transfer devices perform satisfactorily, certain problems can be encountered during their use. For example, unless some mechanism is provided for moving the pan extractor horizontally on the elevator to a position closely adjacent the pan, extremely close tolerances must be maintained between the elevator and storage racks and pan stored therein. This close tolerance requirement throughout the entire warehouse system is difficult to maintain and should only one pan or rack be out of alignment a small amount, serious problems and equipment damage can result.
Another problem is that most retrieval devices will only hold one pan or load at any one time requiring the shuttle to return all the way to a home position for discharging the retracted pan before returning to the warehouse for retrieval of a second pan. Depending upon the size of the warehouse installation, this requires the shuttle to travel a considerable distance each time. Likewise, the shuttle must retrace its path many times in performing pan transfer functions.
Another problem is that the article storage pans used in automatic warehouse systems are generally formed of rigid expensive metal components to ensure long life due to their repeated handling by the transfer device and personnel at a load control station in the warehouse. Such pan replacement is expensive and increases the cost of the warehouse operation. Even though only a small part of the pan may be bent or damaged, it will require replacement of the entire pan.
Accordingly the need has existed for an improved pan transfer device for use in moving a storage pan between a storage compartment and a shuttle in which a plurality of pans may be accumulated on the shuttle during movement of the shuttle, in which the transfer device is moved horizontally toward and away from the storage compartment when transferring a pan between the elevator and storage compartment thereby eliminating the heretofore close tolerances between the elevator and storage racks; and in which an inexpensive pan can be used with the improved transfer device.